1. Field of the Invention
This invention generally involves control valves and more particularly involves a pressure-activated control valve.
2. Description of Related Art
A control valve is a final controlling element that directly changes the value of the controlled variable in an automatic control system by varying the rate of flow of some fluid or gas. The control valve is well-known in the control arts and has been defined as a continuously variable orifice in a fluid-flow line. The complete control valve consists of an actuator and a valve body. The actuator provides the power to vary the port opening in the valve body. The valve body assembly consists of a pressure-tight chamber that is fitted into a pipeline.
Control valves are often classified on the basis of the means of actuation as pneumatically, hydraulically or electrically operated valves. Electrical actuators for control valves are also often categorized into two basic categories: inherently two-position actuators, including solenoids and relays, and inherently infinite-position actuators, including reversible electric motor drives, saturable-core reactors, silicon-controlled rectifiers, variable-speed electric motor drives, and electropneumatic convertors. Each of these well-known types of devices requires an external compressed air or AC line power supply. All have many moving parts contributing to wear and eventual failure and are not generally suitable for application to microminiature control systems operating from limited power supplies.
An electrochemical cell is typically formed by positioning a rigidly-supported electrolytic membrane between and in contact with a cathode and an anode. Such a cell can either generate electricity (chemical to electrical) or do mechanical work (electrical to mechanical). When the cell is configured as a "fuel cell" to generate electricity, a fuel gas such as hydrogen is supplied to the anode and a gaseous oxidant such as oxygen is supplied to the cathode. When the cell is configured as a motor to produce mechanical energy, an electrical voltage is applied across the anode and cathode, and an electrochemically active gas (capable of entering into an oxidation/reduction reaction) is supplied to the anode. At the anode, the gas is ionized and the ions travel across the electrolytic membrane in response to the voltage gradient across the membrane. At the cathode, the ions are reconverted to molecules of the gas, thereby increasing the pressure on the cathode side and decreasing the pressure on the anode side of the membrane. The result is a pumping action across the membrane from anode to cathode. U.S. Pat. No. 4,402,817 issued to Henri J. R. Maget on Sept. 6, 1983 discloses such a single cell used as a prime mover. The absence of moving parts other than a flexible bellows or diaphragm permits many useful embodiment,,s as disclosed in copending patent application Ser. No. 07/563,050 titled "Efficient Electrochemical Motor" filed concurrently herewith.
The application of the electrochemical motor as a valve actuator is unknown in the art. Because the electrochemical motor can operate continuously over a wide dynamic range (e.g. 250 to 1) and with precision unavailable in an electromechanical motor, which tends to stall at low speeds, the electrochemically actuated control valve represents a new class of electrically actuated control valves. There are unresolved problems and deficiencies clearly felt in the art, which are solved by the present invention in the manner described below.